I've done a fair amount of reading no sew tutu instructions and had read conflicting advice. On the one hand I'd read you should add an inch to account for the 1/2 overlap when sewing. On the other hand I'd read that there will be some stretching, as much as an inch or so. Which is consistent with your experience.

But nothing prepared me for the possibility that I'd gain 3" about 1/3 to 1/2 of the way through adding the tulle.

I'd be concerned that I was doing something drastically wrong but believe it or not the elastic with tulle on it still has some stretch left.

This project is salvageable. I just want it to be easier, with less waist (no pun intended) the next time around.